This invention relates generally to folding chairs, and more particularly, to a molded resin folding chair.
Folding chairs are well known in the art, but are most commonly made from metal or wood, and are thus more costly to manufacture. A folding chair typically is constructed of a pair of uprights which are generally parallel and spaced apart from each other, being joined together by one or more cross pieces, which also form the seat back. Other parts of the folding chair include a pair of struts, also generally parallel, spaced apart from each other, and joined by one or more cross pieces. Upper ends of the struts are engaged with the seat whereas the lower ends of the struts support the folding chair in conjunction with the lower ends of the uprights. At points generally intermediate the upper and lower ends, the struts are rotatably attached to the uprights. A back region of the seat is engaged with the uprights at points intermediate the backrest and the lower ends of the upright. Depending on the configuration of the particular folding chair, the seat may be slidably engaged with the uprights to facilitate folding the chair into a configuration wherein the seat, struts, and uprights assume a somewhat parallel relationship with each other so the that chair will fold as flat as possible.
With the advances in the plastic molding industry in recent times, it has become possible to mold many items from resins, such as polypropylene, at a much lower cost than manufacturing the item from metal or wood. However, such resins are generally not as rigid as metal or wood. Wood, for example, is about 10 times more rigid than polypropylene. Rigidity is understandably important in the manufacture of folding chairs since the chair must support the weight of a person resting on the seat.
Making a folding chair from resin can be also more difficult because of problems particularly associated with resin molding processes. Since molded resin is generally less rigid than metal or wood, the frame members of the chair must be configured for structural rigidity. However, molding shapes which have good structural rigidity can present manufacturing problems. For example, one known prior art plastic folding chair utilizes tubular legs having a channel formed adjacent the tubular portion. Although this structure has good structural rigidity, there can be significant problems associated with the molding of tubular legs. In particular, for example, a hollow tubular chair leg can require the use of a core member about which the tube is molded. After molding the tubular part this core member must be removed, which requires a relatively long xe2x80x9cprongxe2x80x9d member to perform the removal. A prong member of such length can create significant maintenance problems. Another problem with molding tubular parts is that shrinkage and warping commonly occur after the tubular part is removed from the mold and begins cooling. Typically, this results because some parts or sides of the tube will cool faster than others, causing the sides of the tube to shrink at different rates. This results in warping of the tube. These and other problems must be dealt with when molding chairs from resin, including polypropylene which is commonly used because of its low cost.
Accordingly, it is desirable to provide a resin molded folding chair which is strong, lightweight, and avoids manufacturing problems such as frequent mold maintenance, shrinkage, and warping.
A molded resin folding chair is provided having uprights which are molded with a generally C-shaped channel, in which tab portions on either side of the seat of the folding chair are slidably captured. The uprights are joined by one or more cross pieces positioned at or near the bottom and at or near the top, wherein one or more top cross pieces form a backrest for the folding chair. The chair further has struts which, at an upper end, are rotatably attached to the base or sides of the seat and, at points intermediate the upper and lower ends, are also rotatably attached to the uprights. The struts can also include a cross piece at or near the lower ends thereof. The chair folds by, for example, lifting the back of the seat upwards, causing the tabs on either side of the seat to slide upwards in the C-shaped channel in each of the uprights. In this manner, the front of the seat rotates downwards and the struts rotate inward. The struts rotate about the attachments to both the uprights and the seat, rotating into a position where the struts are as much as possible parallel to the uprights when the chair is folded. The struts can be similarly formed in a simple C-shape. For increased strength, the uprights, and the struts, can further be formed with transverse ribs positioned in, and at spaced apart locations along, the C-shaped channels. In the pertinent locations along the uprights, the transverse ribs can be sized so as not to interfere with the sliding engagement of the seat tabs in the C-shaped channels. Additionally, the uprights preferably have a molded-in curvature. For example, the upper part of the uprights can be formed at an angle to the lower part, with the apex located generally at the point where the seat attaches. This can be done not only to provide a backrest which is more perpendicular when the folding chair is unfolded for use, but also because the built-in curvature can reduce problems associated with shrinkage and warping. Furthermore, the uprights can be tapered from the apex towards the backrest. The curved uprights and position of the seat, backrest and struts enable the chair to stand alone when the chair is in a folded position. The curved shape also provides comfort to the user and strength to the chair.
Other details, objects, and advantages of the invention will become apparent from the following detailed description and the accompanying drawings figures of certain embodiments thereof.